Side curtain air bags are a relatively modern vehicle improvement that significantly increases occupant safety. These air bags extend on the vehicle interior from a hidden location on the roofline downward, when inflated during a collision, to provide protection for a vehicle occupant. Side curtain air bags can improve safety significantly because they are often the only protection provided that is specific for side impact collision events or sideways movement of a vehicle occupant. A single air bag may cover, on one side of the vehicle, only the area where a front occupant is seated or both this area and the area where a rear occupant is seated.
Side curtain air bags typically have a larger inflated volume than other air bag devices in the vehicle. However, inflation of side curtain air bags must still be as instantaneous as possible. To achieve this goal, higher flow rate inflators and/or multiple inflators may be used. Additionally, distribution devices such a throat liners are used to optimally distribute the inflation gas along the length of the air bag so that inflation is fast and generally even. Typically, larger volumes of air are directed to areas farther from the inflator to compensate for the increased time required for gas to reach these areas.
Because side curtain air bags cannot inflate instantaneously, it is possible that the vehicle occupant, sliding laterally during a collision, could be located directly under the air bag as it expands downward from the roofline of the vehicle. The occupant could also be located in this position for other reasons. Either way, instead of being cushioned by the air bag, the occupant could be injured by the expanding air bag forcefully pushing on the top of his/her head. What is desired is a way to protect a occupant already located in an undesirable position when a side curtain airbag has not yet fully expanded into that position.